The invention is directed to a process for the manufacture of composite wood structures, which provides for improved machinability. More particularly, the process comprises combining wood particles with a composition comprising an aqueous protein and diluent dispersion, followed by molding or compressing the combination of wood particles and reactive mixture that allows for better manufacturing and increased efficiency.
Lignocellulosic based composites, such as interior plywood, medium-density fiberboard (MDF), particle board (PB), waferboard and oriented strandboard, are prepared from combinations of a lignocellulosic such as wood, and a binder or binders, also known as resins and adhesives. Composite materials such as oriented strandboard, particle board and flake board are generally produced by blending or spraying lignocellulose materials such as wood flakes, wood fibers, wood particles, wood wafers, strips or strands, pieces of wood or other comminuted lignocellulose materials with a binder composition while the comminuted materials are blended by tumbling or agitating them in a blender, a blow-line or like apparatus. After blending sufficiently to form a uniform mixture, the materials are formed into a loose mat, which is compressed, for example, between heated platens or plates or steel belts to set the binder and bond the flakes, strands, strips, pieces, etc. together in densified form. Conventional processes are generally carried out at temperatures of from about 150° C. to 225° C. in the presence of varying amounts of steam generated by liberation of entrained moisture from the wood or lignocellulose materials. These processes also generally require that the moisture content of the lignocellulose material be between about 2 and about 35% by weight, before it is blended with the binder.
Binder or adhesive compositions which have been used in making such composite wood products include phenol formaldehyde resins, urea formaldehyde resins and isocyanates. See, for example, James B. Wilson's paper entitled, “Isocyanate Adhesives as Binders for Composition Board” which was presented at the symposium “Wood Adhesives-Research, Applications and Needs” held in Madison, Wis. on Sep. 23-25, 1980, in which the advantages and disadvantages of each of these different types of binders are discussed. Historical and more recent protein based adhesives are water based. Various water based adhesives are described in numerous books, articles, and patents. See for example patents describing soy flour based adhesives (such as U.S. Pat. Nos. 7,060,798 and 7,252,735), urea formaldehyde (UF) based adhesives, melamine urea formaldehyde (MUF) adhesives, melamine formaldehyde (MF) adhesives, phenol formaldehyde (PF) adhesives, and poly(vinyl acetate) and poly(ethylene vinyl acetate) adhesives.
Generally, the adhesive comprises a phenol-formaldehyde (PF) resin. Another commonly used resin is a liquid polymeric 4,4′-methylene-bis(phenyl isocyanate) (pMDI). Although aqueous, alkaline phenol-formaldehyde resins show good durability, relatively low cost and relatively low toxicity, they are known to exhibit slower press times and, in general, produce products with higher thickness swell properties than the same products composed of a pMDI binder. Although isocyanate resins can exhibit some enhanced performance, they are more costly than PF resins. An additional drawback to production in manufacturing plants or mills is the huge capital costs associated with the press and associated equipment, including steam generation equipment which provides the heat during the pressing process.
Following the pressing process, the lignocellulosic composite undergoes machining steps which may include cutting, trimming, routering, and/or sanding. Lignocellulosics made with pMDI binder, in particular, are known to produce board products that are difficult to machine as experienced by such things as wear on saw blades, router blades or sander belts, or quality defects on the cut edge or sanded surface.
U.S. Patent Application No. 2013/0005867 A1, describes soy-based adhesives have also been used in composite board manufacture. These include such as, soy flour, soy protein concentrates (SPC), or soy protein isolates (SPI) as the starting material. For simplicity, the present disclosure refers to all soy products that contain greater than 20% carbohydrates as “soy flour”. Soy flour is less expensive than SPI, but also contains high levels of carbohydrates, requiring more complex crosslinking techniques, as crosslinking results in the much improved water resistance of the soy-based adhesives.
Adhesives comprising starches and protein components, such as soy, are described in references such as, U.S. Pat. Nos. 5,523,293, 6,235,815, U.S. Patent Application 2011/0100256, U.S. Patent Application 2013/202905, U.S. Pat. No. 7,960,452 discloses an adhesive made from plant protein and starch and still other references describe sugars or starches being reacted with urea, phenol or sulfite liquor, U.S. Pat. No. 4,525,164 and BE Patent No. 874584.
U.S. Pat. No. 6,214,265 B1, describes a composition for bonding solid lignocellulosic materials. Suitable binder formulations are based on the reactive mixture of an isocyanate and a carbohydrate material. These are both effective and inexpensive, and eliminate health hazards associated with the use of formaldehyde. Carbohydrate materials include, for example, sugars and starches, in the presence or absence of other active materials. These carbohydrates are mixed with a liquid diisocyanate and applied to the wood, which is then pressed to form a composite product.
In some areas of composite board manufacture sugars have been used as extenders or additives, with molasses and starch being named in a laundry list of carbohydrates, GB Patent No. 976491, U.S. Pat. Nos. 3,239,408, 5,905,115
U.S. Pat. No. 8,901,208 B1, describe a composite board made with a bioresin such as protein-based soybean or carbohydrate-derivative from cellulose or starch; and/or a low formaldehyde or formaldehyde free binder. The binder may in-part be based on a reducing sugar or aldehyde containing sugars.
U.S. Pat. No. 4,183,997, describes the bonding of lignocellulosic material by reacting sugars, starches or both in the presence of a catalyst capable of transforming the sugars and starches into a solid, insoluble in water, and an alkaline buffering agent. However, soy flour is not mentioned.
U.S. Pat. No. 4,654,259, describes bonding wood surfaces together using a bonding composition comprising one or more sugars and an aminoplast. Also described is adhesives based on carbohydrates, such as starches and sugars, which are converted to binders by various means.
There is still a need to produce composite board that provides for improved tool wear and edge quality while maintaining acceptable physical and quality standards of the final product. Using the current composition in the manufacture of composite structures may allow for increased production rates by allowing for quicker cutting and trimming of the composite and may provide for decreased down time due to replacing blades.